LCD (Liquid Crystal Display) has been widely used in various electronic products. In addition to the liquid crystal module, the LCD performance also correlates with the reliability of the backlight module. A backlight module comprises a set of lamps and an inverter. The inverter should provide a longtime stable current. Basically, an inverter receives a DC input and electronically converts the DC power into an AC power from the primary side of a transformer to the secondary side thereof. In other words, an inverter converts a DC power into an AC power to drive AC loads, such as CCFL (Cold Cathode Fluorescent Lamp). Inverters may be classified into the Royer type, full-bridge type, half-bridge type and pull-push type. The Royer type inverter is of self-oscillation design and hard to control lamp frequency and lamp current because of the variation of element parameters. In the push-pull type, the power transistors have to withstand double input voltage, but power transistors are more expensive and have an input-voltage limitation. Therefore, the full-bridge and half-bridge inverters are more popular. The half-bridge inverter is simpler and uses only half the power transistors used by the full-bridge inverter. Thus, using the half-bridge inverter is a cost-efficient selection. Refer to FIG. 1 for a diagram schematically showing a conventional inverter architecture used to drive a backlight module. The conventional inverter comprises: a rectifier unit 40 receiving an input power and converting the input power into a DC power, a duty-cycle modulation unit 42 coupled to the rectifier unit 40, a power factor correction unit 41, a half-bridge driving unit 43, and a transformer unit 44. The secondary side of the transformer unit 44 is further coupled to a feedback unit 45. The feedback unit 45 generates and sends a feedback signal to the duty-cycle modulation unit 42 for stabilizing the output. The power factor correction unit 41 receives the input power from the rectifier unit 40 and adjusts the phase difference between the voltage and current of the input power. The duty-cycle modulation unit 42 is coupled to a dimming signal source 3 and receives a dimming signal therefrom. The duty-cycle modulation unit 42 also receives a feedback signal from the feedback unit 45. According to the dimming signal and the feedback signal, the duty-cycle modulation unit 42 generates a duty-cycle signal to determine the duty cycle of the half-bridge driving unit 43. Thus is modulated the timing that the half-bridge driving unit 43 is turned on to allow the input power to flow toward the transformer unit 44. Then, an AC driving power is generated to drive at least one load 2. The half-bridge driving unit 43 uses the switching of power transistors to modulate the turn-on timing. To achieve zero-voltage switching and reduce the loss at two sides of the power transistors, the half-bridge driving unit 43 has to limit the duty cycle to meet the condition for zero-voltage switching. However, a conventional inverter usually has to generate a feedback signal to change the duty cycle of the half-bridge inverter so that the inverter can provide stable output to drive the load 2. Thus, the half-bridge inverter is often unable to work under the condition for zero-voltage switching, and the physical working efficiency thereof is often lower than the ideal efficiency. The prior arts disclosed in R.O.C. patents No. I273764, No. I242177, R.O.C. publication patent No. 518633 and a U.S. Pat. No. 6,995,989 are all the likes of the abovementioned inverter. The conventional backlight module inverters usually adopt a burst mode dimming, wherein the lamps are repeatedly turned on and off. Such a method indeed attains a satisfied dimming. However, the power source providing the input power and the transformer of the inverter generate low-frequency noise because the inverter has to pulse the output thereof. The low-frequency noise will cause the discomfort of users. Further, the service lives of the lamps and electronic elements are decreased. Besides, EMI (Electro-Magnetic Interference) also become severer.